How to recover from FWS and DAG Member failure in 2 Node DAG

Recently we had a situation where one of our customer was affected with a malware and most of his servers became unusable. The impact caused the File Witness Servers( a Domain Controller) and one of the Exchange Node from the 2 Node DAG environment to become instable.

So after studying the impact we decided to do the below ;

Remove the Failed Node from the DAG and rebuild it from scratch and attach it to the DAG again.

Change the FWS to another server.

But unfortunately we were not able to proceed as we expected because the cluster service on the remaining node was not able to reach any cluster defined. When I opened the Failover Cluster Manager I was not able to reach or connect it to the DAG Cluster (As it was not able to reach any the Quorum in our case it is the FWS. The same was confirmed by the below command:

cluster node
This will show the failed node as down and the survived DAG node in Joining state

To overcome the problem you have to restart the cluster without quorum to do that type the below command on the Exchange server

net stop clussvc

net start clussvc /fq

Boom .. everything returned normal with Windows Clustering on the remaining node ( you could verify it with the same command ; cluster node) . I was able to connect it to the DAG cluster via the Windows Clustering Manager.